A long-held goal of human medicine has been to treat inherited genetic disorders. Genome editing encompasses the powerful concept of directly correcting mutations in endogenous genes to cure or prevent disease. An emerging example of this approach is the clinical trial of a zinc finger nuclease (ZFN) therapeutic engineered to disrupt CCR5, a co-receptor for HIV (1). This ex vivo autologous cell therapy approach attempts to recapitulate the successful cure of HIV in Timothy Brown, the “Berlin Patient,” who was transplanted with bone marrow cells from an individual bearing homozygous mutations in CCR5. Another recent example is the correction of X-linked severe combined immunodeficiency disorder by gene targeting with ZFNs in hematopoietic stem cells derived from a 6-month old subject (2).
There are four main classes of engineered nucleases: 1) meganucleases, 2) zinc-finger nucleases, 3) transcription activator effector-like nucleases (TALEN), and 4) Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) Cas RNA-guided nucleases (RGN).
However, adoption of these new therapeutic and research tools may depend on a demonstration of their specificity. Understanding and identifying off-target effects in human and other eukaryotic cells will be critically essential if these nucleases are to be used widely for research and therapeutic applications.